1. Field of the Invention
The present invention generally relates to a package, and more particularly to a semiconductor package, wherein the mechanical robustness of a stiffener that can prevent a carrier (e.g. substrate) from warping during subsequent thermal processes. Also, the stiffener can be directly mounted on the carrier by the attaching force of an encapsulant. It is not necessary that the stiffener is attached on the carrier by an extra adhesive, thereby decreasing the processing step of the semiconductor package.
2. Description of the Related Art
Due to chips having high performance are required, a chip package having a thin type substrate is increasingly put in use. For example, the chip package having the thin type substrate is applied to a high-end memory, an application specific integrated circuit (ASIC) and a microprocessor having a high electrical performance demand, a high frequency demand and a high speed demand.
A typical chip package having a thin type substrate includes various conductive and insulating materials which have different coefficients of thermal expansions (CTE). For example, a chip is disposed on an upper surface of a substrate by a wire bonding process or a flip chip bonding process. An encapsulant is adapted to seal the chip and disposed on the upper surface of the substrate. A plurality of solder balls are disposed a low surface of the substrate so as form a conventional ball grid array (BGA) package. However, a thin type substrate has a problem of warping. Due to the different CTE's of various conductive and insulating materials used in the BGA package after the BGA package is packaged, the BGA package having the thin type substrate may be warped seriously during subsequent thermal processes (e.g. a reflow process). The warping of the BGA package may cause the substrate not to be co-plane so as to further have a problem of solder ball joints.
Referring to FIG. 1, U.S. Pat. No. 6,894,229, entitled “Mechanically Enhanced Package and Method of Making Same”, discloses a ball grid array package 100 including a substrate 120, a chip 110 and a stiffener 140. The chip 110 is mounted on the substrate 120. Ridges 146 of the stiffener 140 are attached on support pins 126 of the substrate 120. There is a space defined between the stiffener 140 and the substrate 120 for accommodating the chip 110. An encapsulant 160 is filled in the spacer 150 and covers the stiffener 140. The stiffener 140 includes metal or any other solid material which has an enough mechanically robustness and a relatively high thermal conductivity. The thermal conductivity of the stiffener 140 provides the package 100 with a thermal dissipation path, i.e. the stiffener 140 is acted as a heat spreader. The mechanical robustness of the stiffener 140 prevents the substrate 120 from warping during subsequent thermal processes.
Although the reference of U.S. Pat. No. 6,894,229 discloses that the stiffener 140 is adapted to be acted as a heat spreader and to increase the mechanical robustness of the substrate 120, the stiffener 140 needs to cover the whole area that the chip 110 is disposed on so as to affect the layout of other components (e.g. passive components). Furthermore, the height of the stiffener 140 (i.e. the heat spreader) must be higher than that of bonding wires 130 of the chip 110 so as to prevent the bonding wires 130 of the chip 110 from damage. In addition, the stiffener 140 must be attached on the substrate 120 by an adhesive 136.
Referring to FIG. 2, U.S. Pat. No. 6,284,569, entitled “Method of manufacturing a flexible integrated circuit package utilizing an integrated carrier ring/stiffener”, discloses a flexible integrated circuit package 200 including a carrier ring 240. The carrier ring can provide a stiffening function for assembling flexible circuits. A matrix of chips 210 are attached on a substrate 220. The carrier ring 240 is attached on the substrate 220 by an adhesive 236, and is provided with mold gates and mold vents for use in a transfer molding step when an encapsulant 260 seals the chips 210. The height of the carrier ring 240 can control that of the encapsulant 260, and thus provides the chips 210 with a predetermined encapsulation thickness.
However, the height of the carrier ring 240 must be higher than that of the chip 210, whereby the predetermined encapsulation thickness of the chips 210 cannot be less than the height of the chips 210. In addition, the carrier ring 240 must be attached on the substrate 220 by an adhesive 236.
Accordingly, there exists a need for a semiconductor package capable of solving the above-mentioned problems.